1. Field of the Invention
This invention pertains to networks of digital devices with shared components, which networks in turn may share components at a higher level. The interconnections are constructed from two kinds of speed independent switches called arbiters and selectors.
Communication in networks connected by arbiter and selector switches is in the form of serially transmitted messages which in the general case consist of three parts: destination address, body, and source address. The source address originates on the path where it is determined by the arbiter switches from the destination to the source. The destination address selects the path through the network to the destination and is used bit-by-bit in the selector switches along that path. In general, as a message moves through a network, an arbiter appends a bit to indicate through which of its two inputs a message entered and a selector removes the leading bit and selects through which of its two outputs the message leaves. A receiving device accepts first the message body and then the source address.
A speed independent selector has been described in the above referred-to Clark patent application Ser. No. 035,411, and networks in which it may be employed have been described in the above referred-to Barton et al patent application Ser. No. 035,314. The selector described in the present application constitutes an improvement over that described in Ser. No. 035,411.
It is an object of the present invention to provide an improved speed independent selection switch for digital communication networks requiring fewer wires per communication path.
It is another object of the present invention to provide a selector switch which allows clearing of a communication path from the sender towards the receiver as soon as the message has traversed the switch.
It is another object of the present invention to provide a selector switch with a simpler communication protocol.
2. Summary of the Invention
The present invention is a speed independent selection switch designed for pipelined message transmission through digital communication networks. The selector routes a message from the input path to one of two output paths selected by the first bit of the message, that bit then being discarded.
The communication paths each use four wires, three of which are used in a 1-out-of-3 code and the fourth of which acknowledges receipt of a character.
Trees formed from selectors provde distribution to two or more devices from one source.
Networks employing both selectors and arbiters can be formed for the transmission of messages among a number of devices.